ROLE OF PHOSPHOROLYTIC CLEAVAGE IN CELLOBIOSE AND CELLODEXTRIN METABOLISM BY THE RUMINAL BACTERIUM PREVOTELLA-RUMINICOLA

In bacteria, cellobiose and cellodextrins are usually degraded by eith er hydrolytic or phosphorolytic cleavage, Prevotella ruminicola B(1)4 is a noncellulolytic ruminal bacterium which has the ability to utiliz e the products of cellulose degradation, In this organism, cellobiose hydrolytic cleavage activity was threefold greater than phosphorolytic cleavage activity (113 versus 34 nmol/min/mg of protein), as measured by an enzymatic assay, Cellobiose phosphorylase activity (measured as the release of P-i) was found in cellobiose-, mannose-, xylose-, lact ose-, and cellodextrin-grown cells (>92 nmol of P-i/min/mg of protein) , but the activity was reduced by more than 74% for cells grown on fru ctose, L-arabinose, sucrose, maltose, or glucose, a small amount of ce llodextrin phosphorylase activity (19 nmol/min/mg of protein) was also detected, and both phosphorylase activities were located in the cytop lasm. Degradation involving phosphorolytic cleavage conserves more met abolic energy than simple hydrolysis, and such degradation is consiste nt viith substrate-limiting conditions such as those often found in th e rumen.